1. Field of the Invention
The present invention relates to industrial cleaning and polishing technology, and particularly to an apparatus and process for polishing hot strip mill run-out table rolls to remove iron deposits from the rolls.
2. Description of the Prior Art
Modern integrated steel mills include a hot strip mill for processing preheated steel slabs into coils. To form steel coils, steel slabs are first introduced into slab preheating furnaces located at one end of the hot strip mill. The resulting preheated slabs then travel over a large number of table rolls in the direction of a scale breaker, after which the slabs travel through either a reversing rougher mill or several continuous roughing mills.
The roughing mills typically reduce the thickness of the slabs from 8" to 10" to 3/4" to 1",producing "hot strips" of steel. The hot strips then travel toward a series of finishing stands. A hot strip mill usually includes five to seven finishing stands, each finishing stand consisting of two work rolls and two back-up rolls. The work rolls in a finishing stand must be frequently replaced (two to three times in an eight hour shift), due to the rapid roll surface deterioration which occurs during rolling. The finishing stands further reduce the thickness of the hot strips. The last finishing stand does not significantly reduce the thickness of the hot strips, but establishes the final shape of the surface of the hot strips. At this stage in the processing, the hot strips remain in a plasticized state.
Between the last finishing stand and the downcoiler, where the hot strips are formed into coils, there are approximately 300 to 500 run-out table rolls. The hot strips are transported by the run-out table rolls at high speed (40 to 60 miles per hour) in the direction of downcoiler pinch rolls. The downcoiler pinch rolls grab the hot strips, and direct the leading nose of the hot strips toward a coil-making apparatus. Substantial tension is developed between the downcoiler pinch rolls and the coiler to assure the making of tight coils. While the hot strips are traveling over the numerous run-out table rolls, the hot strips are cooled by water sprayed onto the hot strips from above and below.
Since the plasticized hot strips travel over the run-out table rolls at relatively high speeds, iron deposits tend to build up on the surface of the run-out table rolls. The iron deposits often mark up the surface of the hot strips to such an extent that the hot strips cannot be used to manufacture consumer goods.
To remedy this problem, hot strip mills are periodically shut down so that the several hundred run-out table rolls can be hand-ground to clean off the accumulated iron deposits. Hand-grinding poses a significant danger to laborers, however, because the run-out table rolls must be motor-driven while the hand-grinding process is carried out. Moreover, hand-grinding is a time-consuming task which results in an unrecoverable loss of eight to sixteen hours of production every time the mill must be shut-down to clean the run-out table rolls.
Modern hot strip mills are capable of producing three to five million tons of steel coils per annum at a cost of several hundred dollars per ton of steel. However, the poor quality of the manufactured coils resulting from damage caused by iron deposits on the table rolls, and the loss of productivity associated with periodic hand-grinding of the rolls, presently cost hot strip mills tens of millions of dollars per year.
In this regard, a number of hot strip mills have been permanently closed over the past two decades due to lost productivity and the inability of the mills to meet quality demands placed on them by the automobile and other industries. The annual world-wide production of hot-rolled steel coils has in fact been substantially reduced, resulting in a shortage of hot-rolled coils that is projected to continue into the future.
Domestically, a number of hot strip mills have been modernized at a cost of 200 to 300 million dollars each. The projected cost for a new, state-of-the-art hot strip mill is between 500 million and one billion dollars. It can take five to seven years to complete the construction of a new mill. In view of these costs, there are presently no known plans to build a new hot strip mill anywhere in the world. Accordingly, substantial demands have been placed on existing hot strip mills to reach their maximum production capacities. Increasing mill productivity by just 1/2%, for example, would result in millions of dollars in savings per annum.